1. Field of the Invention
The present invention relates to a fuel cell system, and more particularly, to a power supply apparatus and method for a line connection type fuel cell system which improves the operating efficiency of the fuel cell system by stably supplying power to a power converter system (PCS) control board when the fuel cell system is initially started.
2. Description of the Background Art
In general, a fuel cell is an apparatus which generates electric energy from fuel.
In an example of a fuel cell, an anode and a cathode are installed at both sides of a polymer electrolyte film. Electrochemical oxidation of hydrogen, which is a fuel, is generated at the anode (also referred to as an oxidation electrode), and electrochemical deoxidation of oxygen, which is an oxidizing agent, is generated at the cathode (also referred to as a deoxidation electrode).
The fuel cell generates electrons by the electrochemical oxidation and deoxidation, and generates electric energy by movement of the electrons.
Exemplary fuel cells include a phosphoric acid fuel cell, an alkaline fuel cell, a proton exchange membrane fuel cell, a molten carbonate fuel cell, a solid oxide fuel cell, and a direct methanol fuel cell.
Exemplary applications of fuel cells include a commercial fuel cell, a home fuel cell, a vehicle fuel cell for an electric vehicle, and a small-sized fuel cell for a portable terminal or a notebook computer.
The home fuel cell has been improved to efficiently operate an electric home appliance or a lighting apparatus in a house. The commercial fuel cell has been improved to efficiently operate a lighting apparatus, a motor or a machine in a shopping center or a factory.
A fuel cell system may connect to a line power supply system, such as that of an electric power utility. If power supplied by a fuel cell system to a load is deficient, the fuel cell system is supplied with the deficient quantity of power from the line power supply system. If power supplied by the fuel cell system to the load is excessive, the fuel cell system supplies the excess power to the line power supply system.
FIG. 1 is a block diagram illustrating a conventional power supply apparatus for a line connection type fuel cell system.
Referring to FIG. 1, the conventional power supply apparatus includes a fuel cell 1, a DC/DC converting unit 2, an inverter 3, a line power supplying unit 4, a balance of plant (BOP) power supplying unit 5, and a power converter system (PCS) control power supplying unit 6.
A rectifier in the inverter 3 (not shown), converts AC line power outputted from the line power supplying unit 4 into DC line power. When the fuel cell system is initially started, the BOP power supplying unit 5 receives the DC line power, converts the DC line power into BOP power having a predetermined voltage level, and supplies the BOP power to BOP components of the fuel cell system.
Exemplary BOP components include an air supplying device (such as, but not limited to, for example, a compressor, pump, etc.) which supplies oxygen to the fuel cell 1, and a fuel supplying device which supplies fuel to the fuel cell 1.
The fuel cell 1 generates DC power by reacting the oxygen from the air supplying device (not shown) and fuel from the fuel supplying device (not shown).
The DC/DC converting unit 2 boosts the voltage of the DC power generated by the fuel cell 1, and outputs the boosted DC power.
The inverter 3 converts the DC power outputted from the DC/DC converting unit 2 into an AC power, and supplies the AC power to at least one load.
A triac Tr, which is turned off when the fuel cell system initially starts and is turned on after the fuel cell system starts, and a charging resistor CR, which is connected in parallel to the triac Tr to control charging of a DC link voltage, are connected between an output terminal of the inverter 3 and a line power line.
During initial starting, the PCS control power supplying unit 6 receives the DC line power, converts the DC line power into PCS control power having a predetermined voltage level, and supplies the PCS control power to a PCS control board (not shown) as operating power.
The operation of the conventional power supply apparatus for the line connection type fuel cell system will now be explained.
A controller (not shown) turns off the triac Tr according to a starting command of the fuel cell system. Then, the line power, outputted by the line power supplying unit 4, passes through the charging resistor CR and is supplied to the rectifier in the inverter 3. The rectifier converts the AC line power to DC line power, and supplies the DC line power to a DC link capacitor C to charge the DC link capacitor C.
After the DC link capacitor C is charged to some degree, the BOP power supplying unit 5 receives the DC line power, converts the DC line power to a BOP power having a predetermined voltage level, and supplies the BOP power to BOP components of the fuel cell system.
The PCS control power supplying unit 6 also receives the DC line power, converts the DC line power to a PCS control power having a predetermined voltage level, and supplies the PCS control power to the PCS control board.
Accordingly, the BOP components and the PCS control board are provided with power to generate electricity in the fuel cell 1.
That is, the fuel cell 1 receives fuel and air from the BOP components (not shown), and the fuel and air react together to generate DC power.
Thereafter, the DC/DC converting unit 2 boosts the voltage of the DC power generated by the fuel cell 1, and outputs the boosted DC power to the inverter 3. The inverter 3 converts the DC power outputted by the DC/DC converting unit 2 into an AC power, and supplies the AC power to the load.
A controller (not shown) monitors whether the DC power has been generated by the fuel cell 1. If the controller senses the DC power, the controller makes the triac Tr conductive, thereby transmitting the AC power from the inverter 3 to the load through the conductive triac Tr.
However, the conventional power supply apparatus must charge the DC link capacitor C, which has a large capacitance, when the fuel cell system is initially started, which requires a charging resistor with a large resistance. Accordingly, a large current flows in a short time in the initial starting, thereby shorting out the charging resistor.
In addition, when the DC link capacitor C is charging, power is supplied to the PCS control board, which causes mis-operations of the PCS control board,